Process for the preparation of alkyl nitrates



Dec. 22, 1970 BACHMAN ET AL 3,549,686

. PROCESS FOR THE PREPARATION OF ALKYL NllRA'lI-IS Filed July 29, 1968 ALKYL NITRITE IN *WATER OUT WATER IN WATER our 5 J ALKYLNITRATE I) 1 LAYER MAGNETIC STIRRER 7' 5 INVENTORS GUSTAVE B. BACHMAN NEIL w. comm United States Patent Oflice 3,549,686 Patented Dec. 22, 1970 3,549,686 PROCESS FOR THE PREPARATION OF ALKYL NITRATES Gustave B. Bachman, Lafayette, Ind., and Neil W. Counon, Rochester, N.Y., assignors to Purdue Research Foundation, Lafayette, Ind., a corporation of Indiana Filed July 29, 1968, Ser. No. 748,338

Int. Cl. C07c 77/02 US. Cl. 260-467 12 Claims ABSTRACT OF THE DISCLOSURE A process for preparing alkyl nitrates by contacting an alkyl nitrite, such as octyl nitrite, in liquid form with gaseous dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate and nitric acid, and rapidly removing the alkyl nitrate from the reaction mixture.

SUMMARY OF THE INVENTION This invention relates to a process for the preparation of alkyl nitrates by contacting an alkyl nitrite in liquid form with gaseous dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate and nitric acid, and rapidly removing the alkyl nitrate from the reaction mixture. In a particular aspect, the present invention relates to a process for the preparation of alkyl nitrates by contacting countercurrently a liquid stream of an alkyl nitrite with a gaseous stream of dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate, and removing the alkyl nitrate from the reaction mixture.

Processes for the preparation of alkyl nitrates from alkyl nitrites are known to the art. The preparation of ethyl nitrate by the reaction of ethyl nitrite with ethyl hydroperoxide is described by Baeyer and Villiger in Chemische Berichte, 34, 755 (1901). In an article by Levy and Scaife in Journal of the Chemical Society, 1093 (1946), the reaction of olefins with dinitrogen tetroxide to yield alkyl nitrates is described. This reaction proceeds through the intermediate B-nitroalkyl nitrite.

The methods described in the prior art are generally unsuitable due principally to the production of considerable quantities of unwanted by-products. This not only results in substantial reduction in yields of alkyl nitrate but can present complex recovery problems.

It is an object of the present invention to provide a process for the preparation of alkyl nitrates.

It is a further object of the present invention to provide a process for the preparation of alkyl nitrates from alkyl nitrites wherein the production of unwanted byproducts is minimized.

Other objects and advantages of the present invention will be apparent from the specification and appended claims.

It has been discovered in accordance with the present invention that alkyl nitrates are obtained without the previously discussed drawbacks of prior art processes by contacting an alkyl nitrite in liquid form with gaseous dinitrogen pentoxide to form a reaction mixture containing alkyl nitrate and nitric acid, and rapidly removing the thus formed alkyl nitrate from the reaction mixture.

DETAILED DESCRIPTION The nitration reaction may be carried out by any suitable procedure. One such procedure involves bubbling gaseous dinitrogen pentoxide through liquid alkyl nitrite. A preferred procedure involves countercurrently contacting a liquid stream of alkyl nitrite and a gaseous stream of dinitrogen pentoxide in a continuous manner. Irrespective of the procedure employed, it is preferred to rapidly remove the alkyl nitrate from the reaction mixture in order to minimize production of unwanted by-products, particularly carboxylic acids.

In a specific embodiment of the present invention, alkyl nitrite in liquid form, such as octyl nitrite, is converted into the nitrate by contact with gaseous dinitrogen pentoxide in an apparatus as illustrated in the single figure. Referring to the figure, octyl nitrite dissolved in carbon tetrachloride is fed into a vertical, spiral reaction column 1 and passes downward and through the column. Simultaneously, gaseous dinitrogen pentoxide is fed into the reaction column and passes upward and into contact with the descending nitrite. Throughout the reaction, the reaction column and its contents are cooled by a jacket of cooling water 2. The resultant reaction mixture containing octyl nitrate and nitric acid flows downward through a tube 3 into a quenching vessel 4 where it is mixed with water. The water serves both as an extractant and as a quenching agent, thereby minimizing the possibility of reaction between the alkyl nitrate and the nitric acid and any other reaction products formed before and during separation of the alkyl nitrate from the reaction mixture. As the process proceeds, a liquid mixture of water and reaction mixture is continuously drawn ofl? through a line 5 to a separation vessel 6. Throughout the process, additional water is continuously passed into the quenching vessel. The liquid mixture in the separation vessel separates on standing into an upper octyl nitrate layer and a lower water layer. Continuous removal of the octyl nitrate layer from the water layer is accomplished by drawing the octyl nitrate off through a line 7 to a collection vessel, not shown. The aqueous layer is continuously removed through a line 8.

The reaction vessel employed in the process of the present invention together with most of the associated lines and equipment is preferably made of or lined with acid resistant materials, owing to the generally corrosive nature of the products under the conditions employed. Glass is especially well suited for this purpose because of its excellent resistance to corrosive materials.

It is to be distinctly understood that the process of the present invention is not limited to the type of apparatus described herein but may be carried out in any type of apparatus which may be recognized as suitable by those skilled in the art.

The nitration reaction may be conducted over a wide temperature range, with a temperature in the range of from about 70 to about +40 C. being typically employed. Temperatures below about 70 C. are generally not practical because of the slow rate of reaction while temperatures above +40 C. tend to cause substantial decomposition of the reactants and the reaction products, in particular the dinitrogen pentoxide. A temperature in the range of from about 0 to about +30 C. is preferred.

The molar ratio of dinitrogen pentoxide to alkyl nitrite may also be varied over a wide range, with a ratio of dinitrogen pentoxide to nitrite in the range of from about 1.5:1.() to about l.0:l.0 being generally preferred. A molar ratio of dinitrogen pentoxide to nitrite in the range of from about l.2:1. 0 to about 1.1:1.0 is especially preferred.

Any suitable alkyl nitrite may be employed in the process of the present invention. Typically employed alkyl nitrites are the mono and dinitrites having from 1 up to about 20 carbon atoms, as for example ethyl nitrite, pentamethylene dinitrite, tertiary butyl nitrite, cyclohexyl nitrite, tertiary amyl nitrite, cyclopentyl nitrite, secondary butyl nitrite, hexamethylene dinitrite, octyl nitrite, propyl nitrite, 2-chloroethyl nitrite, decyl nitrite, heptyl nitrite, dodecyl nitrite, isopropyl nitrite and the like. Because of the tendency of tertiaryl alkyl nitrite to hydrolyze rapidly in water, it is preferred when employing a tertiary alkyl nitrite as the starting material to avoid contacting the reaction mixture with water. Accordingly, When a tertiary alkyl nitrite is employed, the reaction mixture is preferably added to a suitable non-aqueous, inert solvent for the nitrate and the nitrate is then recovered from solution, as for example by distillation. Examples of suitable solvents include the aliphatic hydrocarbons, such as pentane, hexane, heptane, and the like. The solvent preferably contains a complexing agent for nitric acid which will not react with the alkyl nitrate, such as for example sodium fluoride.

As previously indicated, the alkyl nitrite is employed in liquid form. If desired, as for example when the process is operated at a temperature below the freezing point of the particular alkyl nitrite of choice, a suitable inert solvent for the alkyl nitrite which is liquid at the temperature employed may be used. Examples of such solvents include chloroform, carbon tetrachloride and the lower nitroalkanes, for example nitromethane, nitroethane and nitropropane.

The dinitrogen pentoxide of use in the present invention may be prepared by an suitable procedure, such as for example by the reaction of N with ozone in the known manner.

The invention will be understood more fully by reference to the following specific examples. It is understood that the examples are presented for the purpose of illustration only and are not intended as a limitation of the invention.

EXAMPLE 1 To a three-necked 500 ml. flask equipped with an agitator were charged 50 ml. of carbon tetrachloride. The temperature of the carbon tetrachloride was approximately 0 C. A solution of octyl nitrite (0.20 mole) in 37 ml. of carbon tetrachloride was added dropwise to the carbon tetrachloride in the flask over a four-hour period. Throughout the four-hour addition period, dinitrogen pentoxide was bubbled through the solution. Agitation of the reaction mixture was maintained throughout the addition period. At the completion of the addition period, agitation of the reaction mixture was continued for four additional hours. Throughout the procedure, the temperature of the contents of the flask was maintained at approximately 0 C. by means of an ice bath. Octyl nitrate in a yield of 72% and octanoic acid in a yield of 28% were obtained.

The octyl nitrate is separated from the reaction mixture by distillation.

EXAMPLE 2 The procedure of Example 1 was repeated in all essential details except that the solution of octyl nitrite in carbon tetrachloride and the dinitrogen pentoxide were added over an eight-hour period instead of over a fourhour period. Octyl nitrate in a yield of 71% and octanoic acid in a yield of 29% were obtained.

EXAMPLE 3 Gaseous dinitrogen pentoxide and a solution of octyl nitrite in carbon tetrachloride are fed continuously to an apparatus as illustrated in the figure over a period of six hours. The nitration reaction is carried out at a temperature of approximately 20 C. Octyl nitrate is obtained.

EXAMPLE 4 Essentially the same procedure used in Example 3 is employed except that pentamethylene dinitrite is substituted for octyl nitrite to obtain pentamethylene dinitrate.

4 EXAMPLE 5 Essentially the same procedure used in Example 3 is employed except that cyclohexyl nitrite is substituted for octyl nitrite to obtain cyclohexyl nitrate.

EXAMPLE 6 Essentially the same procedure used in Example 3 is employed except that propyl nitrite is substituted for octyl nitrite to obtain propyl nitrate.

Since many embodiments of this invention may be made and since many changes may be made in the embodiments described, the foregoing is to be interpreted as illustrative only and the invention is defined by the claims appended hereto.

What is claimed is:

1. A process for the preparation of alkyl nitrates which comprises contacting an alkyl nitrite in liquid form with gaseous dinitrogen pentoxide, thereby forming a reaction mixture containing alkyl nitrate and nitric acid, and rapidly removing the said alkyl nitrate from the reaction mixture.

2. The process of claim 1 wherein the reaction is carried out at a temperature above about C. but below temperatures causing substantial decomposition of the said nitrate, the said nitrate or the said dinitrogen pentoxide.

3. The process of claim 1 wherein the alkyl nitrite and the dinitrogen pentoxide are contacted countercurrently.

4. The process of claim 3 carried out in a continuous manner.

5. The process of claim 3 wherein the alkyl nitrite comprises a liquid stream and the dinitrogen pentoxide comprises a gaseous stream.

6. The process of claim 2 wherein the temperature is in the range of from about 0 to about 30 C.

7. The process of claim 1 wherein the molar ratio of dinitrogen pentoxide to alkyl nitrite is in the range of from about 1.5:1.0 to about l.1:1.0.

8. The process of claim 7 wherein the molar ratio of dinitrogen pentoxide to alkyl nitrite is in the range of from about 1.2:1.0 to about 1.1:1.0.

9. The process of claim 1 wherein the alkyl nitrite is a mono or dinitrite containing from 1 to about 20 carbon atoms.

10. The process of claim 9 wherein the said nitrite is a primary or secondary nitrite.

11. The process of claim 10 wherein the said alkyl nitrate is removed from the said reaction mixture by adding the reaction mixture to water, permitting the resulting mixture to separate into an alkyl nitrate layer and an aqueous layer and removing the alkyl nitrate layer from the aqueous layer.

12. The process of claim 9 wherein the nitrite is a tertiary nitrite.

References Cited UNITED STATES PATENTS 11/1968 Ohman et a1 260-467 OTHER REFERENCES Boschan et al.: Chem. Reviews, vol. 55, pp. 485-488 (1955).

Rodds Chemistry of Carbon Compounds, S. Coffey, editor, 2nd ed., vol. I, part B, Elsevier Pub. Co., London, 1964, pp. 57-60.

LELAND A. SEBASTIAN, Primary Examiner U.S. Cl. X.R.

my UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. U.S. 3 ,5?! ,686 Dated December 22 19 70 Gustave B. Bachman and Neil w. Connon Inventofls) It is certified that error appears in the ab0veidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, Column 3, Column 4,

line 71 "nitrite" should be -nitrates. I

line 22 "an" should be ---any-. line 25 "nitrate" second occurrence, should be --nitrite--.

Signed and sealed this 6th day of April 1971 (SEAL) Attest:

EDWARD M.FLETGHER,JR. Attesting Officer WILLIAM E. SCHUYLER, JR. Commissioner of Patents 

